Please bear with me here all. I have a pair of JBL 2269 I want to build a pair of subs with. From what I've gathered here and elsewhere is that BR and PR designs can be made to behave identically in terms of final result with a given driver, in this case the 2269.
I've discovered that shorting the driver's + and - connections with a piece of wire causes the vc to seize in the gap. This can help protect it during transport. So I'm wondering if the strength of this counter force can be varied by using a resistor instead of a wire? Further, if a variable resistor with an L-Pad were hooked up, could this then be altered 'on the fly' so to speak? If it could and a driver were substituted for a PR incorporating this system and applied to a BR box instead of a port, could the tuning be tailored for best response in a particular room with the L-Pad while listening?
If this is possible, the substitute driver/PR would not need to be an identical match to the driver making sound, and therefore cost effective, right?
Much appreciated.
I've discovered that shorting the driver's + and - connections with a piece of wire causes the vc to seize in the gap. This can help protect it during transport. So I'm wondering if the strength of this counter force can be varied by using a resistor instead of a wire? Further, if a variable resistor with an L-Pad were hooked up, could this then be altered 'on the fly' so to speak? If it could and a driver were substituted for a PR incorporating this system and applied to a BR box instead of a port, could the tuning be tailored for best response in a particular room with the L-Pad while listening?
If this is possible, the substitute driver/PR would not need to be an identical match to the driver making sound, and therefore cost effective, right?
Much appreciated.
How it that cost effective? Even it it could be used to tune the PR that way (which is an interesting experiment), it works only because there is magnet assembly present. So basically would need a full driver.
It was done many years ago by Sonus Faber I believe, I think the Elector.
(This may be wrong, but I seem to remember a KEF racing track driver being used, and I was considering it on one of my attempts.)
They used a pot to terminate the driver, it giving variable damping, and from memory it only affects the degree of O/P not the frequency at which it operates.
(This may be wrong, but I seem to remember a KEF racing track driver being used, and I was considering it on one of my attempts.)
They used a pot to terminate the driver, it giving variable damping, and from memory it only affects the degree of O/P not the frequency at which it operates.
Is that not how the function of the port is converted to PR, though? I mean would that not serve the same purpose as adding mass?
Sorry, I'm sure it's me who doesn't understand. I thought I understood how a passive radiator works in lieu of a port in a BR cab. Is it not the diameter of the PR X mass/resistance?
My real question here is if this could work, could this method then be useful in tuning the sub to precisely match the requirements of the room for best performance? Does the room have any influence in dictating the best tuning of a BR cab? Does not electronic room correction effectively alter the tuning?
Already talked not long ago, google is your friend 🙂
Building passive radiators
Converting a woofer into a passive radiator
Building passive radiators
Converting a woofer into a passive radiator
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Hi Discopete
The principle of BR and PR is very similar.
PRs best use is when you have a small box and want to tune to a very low frequency.
In such cases a suitable port would be very long, for a given port area (for high output you want a big area port to reduce port velocity and port noise).
It is the mass of air in the port which is part of the resonance system, as is the mass of the PR. As you can have magnitude higer mass of the PR you'll therefore also be able to get a much lower resonance frequency.
I also recall a speaker sold in the 80's at least in DK by HiFi Klubben (today Dali), not sure what brand they where .... maybe an own brand, which used a "passive" with a kind of filter to tune it .... maybe some other DK member can remember 😉
As you have tried placing a resistor across the terminals makes it harder to move the cone .... meaning thet the resonance will have moved upwards. Normally you want/need, a very low resonance freq for the PR .. something like 10-15 Hz in a given box. So normally you will actually add more weight to the PR to achieve this.
A "normal" driver will not have a Fs of 15 Hz and adding a resistor will make it worse.
All in all I think the better option is to use a real PR unit. These are tunable by addition og weight.
Also remember that the PR unit needs to be capable of mowing around twice as much air as the driver, theis either requires a larger PR, a PR with higher Xmax or 2 PRs for one driver.
/Baldin
The principle of BR and PR is very similar.
PRs best use is when you have a small box and want to tune to a very low frequency.
In such cases a suitable port would be very long, for a given port area (for high output you want a big area port to reduce port velocity and port noise).
It is the mass of air in the port which is part of the resonance system, as is the mass of the PR. As you can have magnitude higer mass of the PR you'll therefore also be able to get a much lower resonance frequency.
I also recall a speaker sold in the 80's at least in DK by HiFi Klubben (today Dali), not sure what brand they where .... maybe an own brand, which used a "passive" with a kind of filter to tune it .... maybe some other DK member can remember 😉
As you have tried placing a resistor across the terminals makes it harder to move the cone .... meaning thet the resonance will have moved upwards. Normally you want/need, a very low resonance freq for the PR .. something like 10-15 Hz in a given box. So normally you will actually add more weight to the PR to achieve this.
A "normal" driver will not have a Fs of 15 Hz and adding a resistor will make it worse.
All in all I think the better option is to use a real PR unit. These are tunable by addition og weight.
Also remember that the PR unit needs to be capable of mowing around twice as much air as the driver, theis either requires a larger PR, a PR with higher Xmax or 2 PRs for one driver.
/Baldin
I might of course be wrong ... it's so many years ago, but the speaker I was referring to was called "Højttaler +1" and was and own HiFi Klubben brand
See here (no 128)
http://www.worldofhifi.dk/?page=galleries&album=hele_hi-fi_aarbogen-84&img=9755
.... whether anyone can find more on the PR concept is a good question ....
See here (no 128)
http://www.worldofhifi.dk/?page=galleries&album=hele_hi-fi_aarbogen-84&img=9755
.... whether anyone can find more on the PR concept is a good question ....
Ok ... here you go ...
http://www.sandcastle.dk/artikler/HT_bog.pdf
... page 46
Is there anything you can't find on the internet these day? 🙂
http://www.sandcastle.dk/artikler/HT_bog.pdf
... page 46
Is there anything you can't find on the internet these day? 🙂
Thanks. I see my thread is already on that page😀. I hope the info I'm looking for is here. It's not just about the conversion here, it's more the sub/room optimization I'm interested in. Otherwise I see no useful purpose.
I understand your point. So the function would be to start with a lower than optimum frequency and then tune it upward.
Ah, so adding resistance is not the same as adding mass. It could be useful in matching the Q of the driver to the tuned box precisely. But not to change the tuning. Alright then🙂
Is what not the diameter of the PR X mass/resistance?
The precise area of the ABR is not at all critical, but if it had no mass it would need to be equal in diameter to the port design.
However all passives have mass, and this is substantially more than a usual air mass involved in a reflex port. (My last passive had to be loaded with an additional 75g, a probable total of over 100g).
Mass always compromises transient response, but as I have pointed out to critics, transients are usually defined by the harmonics of bass notes, and they are not handled by the passive.
I like passives, especially because I have heard so much muck, (rear cone energy at mid frequencies), and chuffing coming out of ports, even on 100lt pro monitors.
You ask about precise tuning. Adjustment of the quantity of O/P is facilitated by the adjustable R placed across the passives terminals, but the frequency at which the passive operates will remain the same.
The quantity adjustment may allow better room matching, but won't affect eigentone frequencies separately from other frequencies. Peaks and troughs will all be affected, increased or decreased.
Even though the R does 'stiffen' the compliance of the passive, I don't think it changes the resonant frequency, and it results in a loss of energy converted to heat in the R.
An ABR is quite a wide band device, more so than a port.
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Think you are absolutely right .... bit stupid of me .... resistors do not change frequency, they dampen 😉
By using an LC network like in the +1 speaker you would be able to place a notch at some frequency
Could be fun to try out 😉